1. Field of the Invention
The invention relates to a coolant conduit comprising a plurality of polymer layers that has a high resistance to hydrolysis and a high pressure resistance which conveys a high bursting strength. In particular, the invention relates to a coolant conduit which is an elongate tubular article for an apparatus such as as engine, especially a motor vehicle engine.
2. Description of the Related Art
Coolant conduits are not simple in form as a rule but rather are more likely to have bizarre shapes. They are often constructed of metal parts and elastic adaptors to compensate for the sometimes intense vibration of the motor. In accordance with the prior art, rubber coolant conduits reinforced with woven fibers (textiles) have been used for this purpose. Such rubber conduits have been preferably used for vehicle engines, but have the disadvantage that they are relatively expensive and, despite this, do not completely fulfill the requirements made of them, particularly with respect to stability at high temperatures, such as the high temperatures arising in an engine compartment. The mechanical properties of such rubber coolant conduits deteriorate sharply after a period of operation equivalent to approximately 100,000 km traveled. Stability of rubber coolant conduits will become even more critical for future automobile engines, which allow the temperatures in the engine compartment to rise even higher than before, thus accelerating deterioration in the mechanical properties of such rubber coolant conduits.
Coolant conduits made of a single polymer layer, so-called "monotubes", have thus far found only limited opportunities for use. At temperatures above 100.degree. C., monotubes made of polyolefins exhibit an inadequate pressure resistance. At temperatures above 100.degree. C., monotubes made of polyamides exhibit a reduced resistance to hydrolysis.
For this reason, polyamides reinforced with glass fibers have been used for parts that come into direct contact with coolant since the glass fibers can partly compensate for the loss of mechanical properties of the polyamides, for instance from swelling. Glass fiber reinforced tubes are not flexible, however.
Simple, tubular, multilayer coolant conduits are known and have been made by coextrusion in accordance with European Patent No. 0 436 923 A2, the disclosure of which is incorporated herein by reference. These coolant conduits are flexible but have only limited opportunities for use because of their shape. They are especially suitable for use as adaptors.
It is therefore an object of the present invention to create a coolant conduit that does not have the forenamed disadvantages.